As implantable cardiac stimulation device technology continues to evolve, there is a push to improve and refine the various processes by which such devices collect, process, and use information associated with a patient to effectuate a treatment that best accommodates the individual patient's needs, health and safety.
Cardiac stimulation devices are used to treat a wide variety of cardiac arrhythmias. Cardiac arrhythmias can generally be thought of as disturbances of the normal rhythm of the heart muscle. Cardiac arrhythmias are broadly divided into two major categories, bradyarrhythmia and tachyarrhythmia. Tachyarrhythmia can be broadly defined as an abnormally rapid heart (e.g., over 100 beats/minute, at rest), and bradyarrhythmia can be broadly defined as an abnormally slow heart (e.g., less than 50 beats/minute). Tachyarrhythmias are further subdivided into two major sub-categories, namely, tachycardia and fibrillation. Tachycardia is a condition in which the electrical activity and rhythms of the heart are rapid, but organized. Fibrillation is a condition in which the electrical activity and rhythm of the heart are rapid, chaotic, and disorganized. Tachycardia and fibrillation are further classified according to their location within the heart, namely, either atrial or ventricular.
In general, atrial arrhythmias are non-life threatening, chronic conditions, because the atria (upper chambers of the heart) are only responsible for aiding the movement of blood into the ventricles (lower chambers of the heart), whereas ventricular arrhythmias are life-threatening, acute events, because the heart's ability to pump blood to the rest of the body is impaired if the ventricles become arrhythmic.
Various arrhythmias can be brought on by, or their likelihood of occurrence can be increased in some individuals by so-called “premature events.” Examples of premature events include premature atrial contractions (PACs) and premature ventricular contractions (PVCs) also termed “premature beats”. Premature beats or contractions are beats that occur earlier than expected and briefly interrupt the normal heart rhythm. Premature beats are the most common cause of an irregular heartbeat. Although they tend to be more common in people with heart disease, almost everyone experiences them at least occasionally. Premature beats often cause a sensation of a “skipped beat” or “flip-flop.” What are really felt are not the premature beats themselves but rather the forceful beat that follows the pause after the premature beat. During the pause, the heart has more time to fill with blood making the next beat more forceful. Premature beats are sometimes, but not always, associated with other arrhythmias.
Premature beats may originate from anywhere in the heart. The most common forms of premature beats seen in daily practice are premature contractions originating in the ventricle (PVC) and premature contractions in the atria (PAC).
The presence of premature beats usually is not a major concern. Premature contractions are common in normal individuals. Their presence alone does not require treatment unless they cause intolerable symptoms. Very often, a few changes in lifestyle, such as reducing stress or avoiding caffeine, will be sufficient to regulate the heartbeat. If premature ventricular beats are frequent or occur in certain patterns, they may be indicative of more serious problems.
Because of the increased likelihood of arrhythmias in some individuals who experience premature events such as PVCs and PACs, it can be desirable to treat or administer therapy when such premature events are detected.
One type of treatment or therapy that has developed is rate smoothing therapy. For example, patients typically have a characteristic RR interval. The RR interval is the distance between two successive R-waves, where an R-wave is associated with a patient's heart beat. When a person experiences a PVC, there is typically a compensatory period in which the heart attempts to recover. Some believe that the compensatory period is an attempt by the body's autonomic nervous system to respond to the PVC abnormality.
In many patients who experience an arrhythmia following a PVC, it has been observed that the RR intervals have a characteristic short-long-short pattern. To attempt to avoid PVC-induced or related arrhythmias, various rate smoothing algorithms have been developed to reduce or eliminate the compensatory period and short-long-short pattern. Specifically, these algorithms typically attempt to return a patient to their baseline RR interval as soon as possible. This approach, however, has been observed by some in the field as lacking efficacy in arrhythmia prevention.
Accordingly, this invention arose out of concerns associated with providing improved methods and systems for reducing the likelihood of arrhythmia onset.